The present invention relates generally to a rolling support or suspension system. More particularly, the present invention concerns a rolling support system having canted rolling support members which exhibit very low friction.
Conventionally, rolling support systems utilize generally circular wheels mounted on a horizontal axle for rotation. These wheel-axle assemblies have positive stability against rotation about a horizontal axis perpendicular to the axle. However, the stability of the system to rotation about the axle axis is characterized as neutral. By virtue of this neutral stability, attempted rotations about the axle axis or displacements of the center of gravity for the system perpendicularly to the axle axis are each accompanied by movement of the system to a new point of stability. In addition, the wheel itself is unstable with respect to rotation relative to a horizontal axis through the wheel and perpendicular to the axle. Such a combination of characteristics is frequently considered to be undesirable and requires additional restraints to be built into the system to eliminate this undesired motion.
Another aspect of most conventional rolling suspension systems is the manner in which they carry force loads to the underlying surface: most employ radial bearings rather than thrust bearings. Since rolling elements in low friction radial bearings move into and out of the load bearing zone, there is a cyclical loading on the elements. Moreover, only a small portion of the rolling elements carry the load requiring comparatively large bearings. On the other hand, low friction thrust bearings use all rolling elements simultaneously for supporting the thrust load. As a consequence thrust bearings can be smaller and lighter. But in addition, thrust bearings have lower friction losses since the frictional forces act at smaller radii than comparable radial bearings.
For wheels mounted to rotate about a horizontal axis, the radius or diameter of the wheel controls the resistance to rolling caused by imperfections in the underlying support surface. For example, it will be seen that a one quarter inch vertical obstruction presents a virtually insurmountable obstacle to a wheel having a diameter of one half an inch; on the other hand, that same vertical obstruction of one quarter inch will present only a small perturbation to continuated rotation of a wheel having a diameter of ten inches.
Other kinds of rolling supports include caster assemblies which, when arranged in pairs, are also stable against a rotation about an axis perpendicular to a line connecting the two casters. However, casters are typically designed for rotation about a vertical axis such that horizontal forces cause the casters to assume a position trailing the vertical axis in the direction of movement. Since the load applied to a caster is a generally positioned in alignment with the vertical axis of rotation, these caster assemblies are unstable with respect to rotation about the line connecting the casters.
The foregoing discussion concerning the significance of vertical imperfections in the underlying support surface is particularly exacerbated for the known caster assemblies for the reason that such caster assemblies for the reason that such caster assemblies typically must fit unobtrusively under furniture or other heavy objects and, necessarily, are restricted to fairly small diameters. For example, caster wheels generally have a diameter of four inches or less.
A common rolling support system typically utilizes ball bearings or roller bearings to reduce the friction associated with applied loads normal to the underlying surface. Such bearing assemblies of necessity dissipate energy through sliding friction of the bearing elements relative to races of the bearing assembly. Such losses may be thought of as being associated with the failure to utilize pure rolling contact between all portions of the bearing surfaces and with the failure of various constraints to achieve perfect alignment of the rolling elements relative to the rolling axis of the bearing. Accordingly, higher power is necessary to cause movement of the support assemblies and greater reliance on lubricants and higher rates of wear pertain than would otherwise be experienced if a purer form of rolling contact between the supporting surfaces could be effectively maintained.
Over the years some variety has developed in conventional rolling support systems. For example, there exists a vehicle using inclined elliptical wheels that present a circular elevation. These vehicles track a sinusoidal path and are useful on soft terrain. See U.S. Pat. No. 3,363,713 issued Jan. 16, 1968 to J. E. Blonsky, and U.S. Pat. No. 2,683,495 issued July 13, 1854 to J. F. Kopzeynski. Both of these devices include differential gearing systems to aid negotiation of curved paths.
Vehicular supports with wheels tiltable about a transverse axis and rotatable about a fixed inclined axis are also known, see U.S. Pat. No. 3,001,601 issued Sept. 26, 1961 to E. P. Aghnides and U.S. Pat. No. 912,010 issued Feb. 9, 1909 to Martin.
Varied forms of rolling geometry have also been used in casters. For example, an inclined ground engaging wheel mounted for rotation in a plane oblique to the supporting surface has been used in combination with a conventional circular wheel which rides on an upper surface of the inclined wheel to support a vertical load. See for example U.S. Pat. No. 3,928,888 issued Dec. 30, 1975 to Lapham. Because of its eccentric geometry and the conventional circular wheel, such a device is not however inherently stable in any plane. Moreover, there is sliding contact between a conical bearing surface of the inclined wheel and a cylindrical bearing surface of the horizontally supported wheel.
Another caster assembly has also been disclosed which incorporates an inclined roller that is journal mounted to a caster supporting structure, see U.S. Pat. No. 3,161,907, issued Dec. 22, 1964, to Anthony. In this arrangement, substantial sliding friction is developed by virtue of the journal bearing arrangement. Moreover, there is a substantial identity between the actual radius of the rolling member and its effective radius as seen in the vertical plane. Thus, the caster does not exhibit enhanced advantages with respect to rolling over vertical imperfections in the underlying surface.
In view of the multifaceted discussion presented above, it will now be apparent to those skilled in the art that the need continues to exist for a rolling support system which overcomes problems of the type discussed.